The present invention is directed to novel compounds and pharmaceutical compositions that inhibit the binding of the SDF-1 chemokine (also known as the CXCL12 chemokine) or I-TAC (also known as CXCL11) to the chemokine receptor CXCR7. These compounds are useful in preventing tumor cell proliferation, tumor formation, tumor vascularization, metastasis, inflammatory diseases including, but not limited to arthritis, renal inflammatory disorders and multiple sclerosis, conditions of improper vascularization including, but not limited to wound healing, treatment of HIV infectivity, and treatment of stem cell differentiation and mobilization disorders (see also, co-pending U.S. Ser. No. 10/912,638, 11/407,729 and 11/050,345).
Chemokines are a superfamily of small, cytokine-like proteins that induce cytoskeletal rearrangement, firm adhesion to endothelial cells, and directional migration and may also effect cell activation and proliferation. Chemokines act in a coordinated fashion with cell surface proteins to direct the specific homing of various subsets of cells to specific anatomical sites.
Early research efforts by a number of groups have indicated a role for the chemokine receptor CXCR4 in metastasis and tumor growth. Muller, et al., “Involvement of Chemokine Receptors in Breast Cancer Metastasis,” Nature, 410:50-56 (2001) demonstrated that breast tumor cells use chemokine-mediated mechanisms, such as those regulating leukocyte trafficking, during the process of metastasis. Tumor cells express a distinct, non-random pattern of functionally active chemokine receptors. Signaling through CXCR4 mediates actin polymerization and pseudopodia formation in breast cancer cells, and induces chemotactic and invasive responses. Additionally, the organs representing the main sites of breast cancer metastasis (such as lymph nodes, bone marrow, and lungs) are the most abundant sources of ligand for the CXCR4 receptor.
Using immunodeficient mice, Muller and colleagues succeeded in reducing the metastasis of injected human breast cancer cells by treating mice with an antibody known to bind CXCR4. Their finding suggests that breast cancer metastasis could be reduced by treating a patient with a CXCR4 antagonist.
Bertolini, et al., “CXCR4 Neutralization, a Novel Therapeutic Approach for Non-Hodgkin's Lymphoma,” Cancer Research, 62:3106-3112 (2002) demonstrated a reduction of tumor volume as well as prolonged survival of immunodeficient mice injected with human lymphoma cells treated with anti-CXCR4 antibodies. They interpreted their finding to mean that tumor volume could be reduced by treating a patient with a CXCR4 antagonist.
More recent studies suggest that another chemokine receptor, CXCR7, may also be a target in the treatment of cancer. CXCR7 is preferentially expressed in transformed cells over normal cells, with detectable expression in a number of human cancers. In vitro studies indicate that proliferation of CXCR7 expressing cells can be inhibited by an antagonist of CXCR7. In vivo studies in mice indicate that CXCR7 antagonists can inhibit tumor formation and tumor growth.
The potential importance of CXCR7 is illustrated by an alternative interpretation of the reduction in tumor volume seen by Bertolini and colleagues. This reduction could clearly be the result of an antibody-mediated clearance, and not the result of the anti-CXCR4 antibody as originally believed. In an antibody-mediated clearance, any antibody that recognized a protein on the cell surface of the lymphoma cells would have had the same effect as that attributed to the anti-CXCR4 antibody. Unfortunately, Bertolini and colleagues studies are inconclusive as to whether the observed tumor response was due to antibody-mediated clearance or interaction with CXCR4.
However it is now known that the lymphoma cells used by Bertolini and colleagues express both CXCR4 and CXCR7. SDF-1 is the only ligand for CXCR4. SDF-1 and I-TAC both bind CXCR7. Using anti-SDF-1 antibody, it has now been shown that antagonists of CXCR7 are responsible for the reduction in tumor load and increased survival rate. Because SDF-1 is the only ligand for CXCR4, one would expect neutralization of SDF-1 with anti-SDF-1 antibody would be equivalent to the neutralization of CXCR4 with anti-CXCR4 antibody. However, experiments using an anti-SDF-1 antibody demonstrated only a partial reduction in tumor load and an increased survival rate. As a result, CXCR7 is the likely target, as the continued activity appears due to the interactions of the second ligand, I-TAC, with CXCR7.
Until recently, the possible importance of CXCR7 in tumor cell proliferation, tumor growth, and metastasis was unknown. Now, evidence points to the ability of certain CXCR7 antagonists to prevent the growth and spread of cancer, and expression patterns indicate a limited tissue distribution for the CXCR7 receptor which correlates to tumorigenesis.
Moreover, it has been discovered that CXCR7 can serve as a co-receptor for certain genetically divergent human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV), in particular for the HIV-2-ROD, an X4-tropic isolate (Shimizu, N. et al., J. Virol., (2000) 74: 619-626; Balabanian, K., et al., J. Biol. Chem., in press; published on Aug. 17, 2005 as Manuscript M508234200).
Still further, SDF-1, has been described to have a role in the mobilization of hematopoietic progenitor cells and stem cells, and in particular of those cells bearing the CXCR4 receptor, from specific hematopoietic tissues including bone marrow has been described (Hattori, K., et al., Blood, (2000) 97:3354-3360; WO 2005/000333, the disclosure of which are incorporated herein by reference). More recent studies suggest that the CXCR7 receptor may also play a part in stem cell mobilization processes.
In view of the above, it is apparent that compounds that are able to bind specifically to CXCR7 receptors can be useful for treating diseases and other biological conditions that may benefit from such interactions. The present invention provides such compounds along with pharmaceutical compositions and related methods for treatment.